From your comment, it sounds like you're trying to direct the way AdMob chooses ads for your users (by specifying "games" as a keyword, for example, to indicate you want AdMob to show ads for games).
That isn't how the addKeyword
method is meant to work. AdMob already knows a good bit about the interests of your app's users based on which ads they've clicked on in the past. The keywords that you add to an ad request are just one piece of the equation when it comes time to actually pick the ad that gets shown. They're not intended to be a strict filter.
Instead, each time your app requests an ad, AdMob will look at all the info it has at its disposal and choose the ad most likely to be interesting to that user at that moment, and then serve it. The more likely the user is to be interested in the ad, the more useful it is for them, and the more valuable for the advertiser. That generally means happier users and more revenue for you.
If you really want to limit the types of ads shown in your app, you can block categories of ads in the AdMob UI. This is likely to have a negative impact on your revenue, though, since it will limit the number of ads competing for your requests.